CHAPTER V ANALYTICAL METHODS ESTIMATION OF DICLOFENAC. Diclofenac (gift sample from M/s Micro Labs Ltd., Pondicherry)

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1 CHAPTER V ANALYTICAL METHODS ESTIMATION OF DICLOFENAC A UV spectrophotometric method based on the measurement of absorbance at 276nm in phosphate buffer of p H 7.4 was used in the present study of the estimation of diclofenac sodium. Materials: Diclofenac (gift sample from M/s Micro Labs Ltd., Pondicherry) Methanol (Qualigens) Potassium dihydrogen phosphate (Qualigens) Sodium hydroxide (Qualigens) Reagents: Phosphate buffer of p H 7.4 Phosphate buffer of p H 7.4 was made by dissolving 6.8 g of potassium dihydrogen phosphate and 1.56 g of sodium hydroxide in 1000 ml with distilled water. The p H was adjusted to 7.4. Standard solution: 10 mg of diclofenac sodium was dissolved in methanol in 25 ml volumetric flask and the solution was made up to volume with methanol. Procedure: The standard solution of diclofenac was subsequently diluted with phosphate buffer of p H 7.4 to obtain series of dilutions containing 2,4,6,8 and 10 μg of diclofenac sodium per ml of solution. The absorbance of the above dilutions was measured in Elico BL 198 double beam UV Spectrophotometer at 276 nm using phosphate buffer of p H 7.4 as blank. The concentrations of diclofenac and corresponding absorbances are given in 73

2 Table 5.1. The absorbance values were plotted against concentration of diclofenac as shown in Figure 5.1 and this calibration curve was used for the estimation of diclofenac in test samples in all in vitro studies. Validation of method The method was validated for linearity, accuracy, precision and interference by other materials used in the present study. Accuracy and precision (Reproducibility) of the method was studied by analyzing six individually weighed samples of diclofenac. Interference by the other materials was evaluated by preparing a physical mixture of diclofenac and cross linked starch urea in 1:1 ratio and analyzing the samples of mixtures for diclofenac content by the proposed method. 74

3 Table 5.1 Calibration Curve for the Estimation of Diclofenac by UV Spectrophotometric method (Using P H 7.4 Phosphate Buffer) Concentration Absorbance (μg / ml) _ x RSD

4 Absorbance r ² = y = x Concentration ( g/ml) Fig 5.1 Calibration curve for the estimation of Diclofenac 76

5 Discussion: The method obeyed Beer s law in the concentration range of 0 10 μg/ml. Low RSD values (Table 5.1.) ensured reproducibility of the method. The mean error (accuracy) and relative standard deviation (precision) were found to be 0.8 % and 1.6%, respectively. The cross linked starch urea did not interfere in the method of estimation. Recovery of the diclofenac from the physical mixture of drug and polymer was found to be 99.5%. Thus the method was found to be suitable for the estimation of diclofenac contents in various products and in vitro dissolution studies in the present investigation. 77

6 ESTIMATION OF ACECLOFENAC A spectrophotometric method based on the measurement of absorbance at 275 nm in phosphate buffer of ph 6.8 was used in the present study for the estimation of aceclofenac. Materials Aceclofenac (gift sample from M/s Suyaash Labs, Chennai) Methanol (Qualigens) Potassium dihydrogen phosphate (Qualigens) Sodium hydroxide (Qualigens) Reagents Phosphate buffer of ph 6.8: Phosphate buffer of ph 6.8 was made by mixing 250 ml of 0.2 M potassium hydrogen phosphate with 112 ml of 0.2 N sodium hydroxide and making upto 1000 ml with freshly boiled and cooled distilled water. The ph was adjusted to 6.8 Standard Solution 25 mg of aceclofenac was dissolved in methanol in a 25 ml of volumetric flask and the solution was made upto volume with methanol. Procedure The standard solution of aceclofenac was subsequently diluted with phosphate buffer of ph 6.8 to obtain a series of dilutions containing 2, 4, 6, 8 and 10 g of aceclofenac in 1 ml solution. The absorbance of these solutions was measured in Elico-SL 159, UV-Vis Spectrophotometer at 275 nm using phosphate buffer of ph 6.8 as blank. The concentration of aceclofenac and the corresponding absorbances are given in Table 78

7 5.2. The absorbances were plotted against concentration of aceclofenac as shown in Fig Validation of method The method was validated for linearity, accuracy, precision and interference by other materials used in the present study. Accuracy and precision (Reproducibility) of the method was studied by analyzing six individually weighed samples of aceclofenac. Interference by the other materials was evaluated by preparing a physical mixture of aceclofenac and cross linked starch urea in 1:1 ratio and analyzing the samples of mixtures for aceclofenac content by the proposed method. Table 5.2 Calibration Curve for the Estimation of Aceclofenac by UV Spectrophotometric Method Aceclofenac Absorbance Concentration ( g/ml) x RSD (%)

8 Absorbance y = 0.029x R² = Concentration (µg/ml) Fig.5.2. Calibration Curve for the Estimation of Aceclofenac by UV Spectrophotometric Method Discussion: The method obeyed Beer s law in the concentration range of 0 10 μg/ml. Low RSD values (Table 5.2.) ensured reproducibility of the method. The mean error (accuracy) and relative standard deviation (precision) were found to be 0.6 % and 1.2%, respectively. The cross linked starch urea did not interfere in the method of estimation. Recovery of the aceclofenac from the physical mixture of drug and polymer was found to be 99.2%. Thus the method was found to be suitable for the estimation of aceclofenac contents in various products and in vitro dissolution studies in the present investigation. 80

9 HPLC METHOD FOR THE ESTIMATION OF DICLOFENAC IN PLASMA Plasma concentrations of diclofenac were determined by an HPLC method developed by Chowdary, K. P. R. and Murali Krishna M. N 1. as follows Instrumentation: The following system is used. The HPLC system (make: M/s Shimadzu Corporation, Japan.) consisted of UV- Visible detector (Shimadzu, Model: SPD 10 AVP), C-18 column (Phenomenex, DESC: Gemini 5 µ C A, Size: 250 x 4.6 mm, S/No: ), 2 pumps (Model: LC 10 ATVP) and a microsyringe of capacity 25 µl (model: Microliter # 702, Mfd: M/s Hamilton). Mobile Phase: The mobile phase is a mixture of acetonitrile: 0.01M potassium dihydrogen phosphate (ph 6.3) (50:50). The mobile phase was filtered through 0.45 µ membrane filter before use and was run at a flow rate of 1 ml/min. Detection: The column effluent was monitored at 276 nm. Estimation of Diclofenac in plasma: For the estimation of diclofenac in plasma samples, a calibration curve was constructed initially by analyzing plasma samples containing different amounts of diclofenac as follows. To a Series of tubes containing 0.5 ml of plasma samples in each, 0.1 ml drug solution containing 1, 2, 4 and 6 µg of diclofenac were added and mixed. To each tube 1 ml of acetonitrile was added, mixed thoroughly and centrifuged at 5000 rpm for 20 min. The organic layer (0.5 ml) was taken into a dry tube and the acetonitrile was evaporated. To the dried residue 0.5 ml of mobile phase [a mixture of acetonitrile: 0.01M potassium 81

10 dihydrogen phosphate (ph 6.3) (50:50)] was added and mixed for reconstitution. Subsequently 20 µl were injected into the column for HPLC analysis. The plasma concentrations of diclofenac and the corresponding peak areas are given in Table 5.3. This calibration curve (Fig. 5.3) was used for the estimation of diclofenac in the plasma samples collected in the pharmacokinetic evaluation. Table 5.3 Calibration Curve for the Estimation of Diclofenac in Plasma Samples by HPLC Method Diclofenac Concentration (µg/0.5 ml of plasma) Mean Peak Area (m V. s) RSD (%)

11 Area (mv.s) r ² = y = x plasma concentration ( g/ml) Fig. 5.3: Calibration curve for the Estimation of Diclofenac in Plasma Samples by HPLC Method REFFERENCES 1. Chowdary, K.P.R. and Murali Krishna M.N., Asian Journal of Chemistry (in press). 83